Thermodynamic Evaluation of the system Ta–O and Preliminary Assessment of the Systems Al–Nb–O and Al–Ta–O

The binary tantalum–oxygen system is assessed using the CALculation of PHase Diagrams (CALPHAD) method with experimental data from the literature. The oxygen solubility in the Ta solid-solution phase is discussed and modeled. The low- and high-temperature modifications of Ta₂O₅ are described as stoichiometric compounds. This dataset is extended into the ternary Al–Ta–O system by complementing it with binary datasets for Al–O and Al–Ta from the literature and adding mixed-oxide AlTaO₄. The dataset for the ternary system Al–Nb–O is created by combining the three corresponding binary datasets from the literature and by assessing the quasibinary section Al₂O₃–Nb₂O₅. The ternary aluminum niobates are described as stoichiometric compounds. Phase equilibria between refractory metals and alumina at high temperature are discussed

Entropy Drives Calcium Carbonate Ion Association

The understanding of the molecular mechanisms underlying the early stages of crystallisation is still incomplete. In the case of calcium carbonate, experimental and computational evidence suggests that phase separation relies on so-called pre-nucleation clusters (PNCs). A thorough thermodynamic analysis of the enthalpic and entropic contributions to the overall free energy of PNC formation derived from three independent methods demonstrates that solute clustering is driven by entropy. This can be quantitatively rationalised by the release of water molecules from ion hydration layers, explaining why ion association is not limited to simple ion pairing. The key role of water release in this process suggests that PNC formation should be a common phenomenon in aqueous solutions

Short-Range Structure of Amorphous Calcium Hydrogen Phosphate

Copyright © 2019 American Chemical Society. Calcium orthophosphates (CaPs) are the hard constituents of bones and teeth, and thus of ultimate importance to humankind, while amorphous CaPs (ACPs) may play crucial roles in CaP biomineralization. Among the various ACPs with Ca/P atomic ratios between 1.0-1.5, an established structural model exists for basic ACP (Ca/P = 1.5), while those of other ACPs remain unclear. Herein, the structure of amorphous calcium hydrogen phosphate (ACHP; Ca/P = 1.0) obtained via aqueous routes at near-neutral pH values, without stabilizers, was studied by experiments (mainly, TEM with ED, XRD, IR, and NMR spectroscopies, as well as XAS) and computer simulation. Our results globally show that ACHP has a distinct short-range structure, and we propose calcium hydrogen phosphate clusters (CHPCs) as its basic unit. This model is consistent with both computer simulations and the experimental results, where CHPCs are arranged together with water molecules to build up ACHP. We demonstrate that Posner's clusters, which are conventionally accepted to be the building unit of basic ACPs, do not represent the short-range structure of ACHP, as Posner's clusters and CHPCs are structurally distinct. This finding is important not only for the determination of the structures of diverse ACPs with varying Ca/P atomic ratios but also for fundamental understanding of a major mineral class that is central to biomineralization in vertebrates and, thus, humans, in particular.

Calorimetric Studies on Chemically Delithiated LiNi0.4_{0.4}Mn0.4_{0.4}Co0.2_{0.2}O2_{2}: Investigation of Phase Transition, Gas Evolution and Enthalpy of Formation

Li1.11(Ni0.4Mn0.4Co0.2)O2 powders were chemically delithiated by (NH4)2S2O8 oxidizer to obtain Lix(Ni0.4Mn0.4Co0.2)O2 powders. The thermal behavior of two delithiated specimens, Li0.76Ni0.41Mn0.42Co0.17O2.10 and Li0.48Ni0.38Mn0.46Co0.16O2.07, was studied compared to the pristine specimen. Phase transitions at elevated temperatures were investigated by simultaneous thermal analysis (STA) and the gas evolution accompanying the phase transitions was analyzed by mass spectroscopy and an oxygen detector. The enthalpy of two delithiated samples and a pristine specimen were measured by a high temperature drop solution calorimeter. Based on these results, the enthalpies of formation were calculated

Mesenchymal stromal/stem cells as potential therapy in diabetic retinopathy

Diabetic retinopathy (DR) is a multifactorial microvascular disease induced by hyperglycemia and subsequent metabolic abnormalities. The resulting cell stress causes a sequela of events that ultimately can lead to severe vision impairment and blindness. The early stages are characterized by activation of glia and loss of pericytes, endothelial cells (EC) and neuronal cells. The integrity of the retinal microvasculature becomes affected, and, as a possible late response, macular edema may develop as a common reason for vision loss in patients with non proliferative DR. Moreover, the local ischemia can trigger vasoproliferation leading to vision-threating proliferative DR (PDR) in humans. Available treatment options include control of metabolic and hemodynamic factors. Timely intervention of advanced DR stages with laser photocoagulation, intraocular anti-vascular endothelial growth factor (VEGF) or glucocorticoid drugs can reduce vision loss. As the pathology involves cell loss of both the vascular and neuroglial compartments, cell replacement strategies by stem and progenitor cells have gained considerable interest in the past years. Compared to other disease entities, so far little is known about the efficacy and potential mode of action of cell therapy in treatment of DR. In preclinical models of DR different cell types have been applied ranging from embryonic or induced pluripotent stem cells, hematopoietic stem cells, and endothelial progenitor cells to mesenchymal stromal cells (MSC). The latter cell population can combine various modes of action (MoA), thus they are among the most intensely tested cell types in cell therapy. The aim of this review is to discuss the rationale for using MSC as potential cell therapy to treat DR. Accordingly, we will revise identified MoA of MSCs and speculate how these may support the repair of the damaged retina

Successful aspiration thrombectomy in a patient with submassive, intermediate-risk pulmonary embolism following COVID-19 pneumonia

A 64-year-old female patient presented with severe dyspnea shortly after apparent recovery from COVID-19 disease. Chest computed tomography revealed central pulmonary embolism and ultrasonography showed a deep vein thrombosis of her right leg. The patient was tachycardiac with evidence of right ventricular strain on echocardiography. An interdisciplinary decision for interventional therapy was made. Angiographic aspiration thrombectomy resulted in a significant reduction of thrombus material and improved flow in the pulmonary arteries and immediate marked clinical improvement and subsequent normalization of functional echocardiographic parameters. This case adds to the emerging evidence for severe thromboembolic complications following COVID-19 and suggests aspiration thrombectomy can be considered in pulmonary embolism of intermediate risk

Introducing the crystalline phase of dicalcium phosphate monohydrate

Calcium orthophosphates (CaPs) are important in geology, biomineralization, animal metabolism and biomedicine, and constitute a structurally and chemically diverse class of minerals. In the case of dicalcium phosphates, ever since brushite (CaHPO4·2H2O, dicalcium phosphate dihydrate, DCPD) and monetite (CaHPO4, dicalcium phosphate, DCP) were first described in 19th century, the form with intermediary chemical formula CaHPO4·H2O (dicalcium phosphate monohydrate, DCPM) has remained elusive. Here, we report the synthesis and crystal structure determination of DCPM. This form of CaP is found to crystallize from amorphous calcium hydrogen phosphate (ACHP) in water-poor environments. The crystal structure of DCPM is determined to show a layered structure with a monoclinic symmetry. DCPM is metastable in water, but can be stabilized by organics, and has a higher alkalinity than DCP and DCPD. This study serves as an inspiration for the future exploration of DCPM’s potential role in biomineralization, or biomedical applications

High‐temperature ternary oxide phases in Ta/Nb‐Alumina composite materials

Coarse-grained composites of refractory ceramics and refractory metals are a novel approach for materials at application temperatures up to 1500 °C. Al$_{2}$O$_{3}$ and the refractory metals Nb and Ta are suitable candidates for enhanced thermal shock capability, as they show similar thermal expansion. During fabrication, a key aspect to consider is the possible formation of additional phases upon interaction of the constituent phases as well as through reaction with the environment. X-Ray diffraction (XRD) and investigations of the microstructure with scanning electron microscopy methods unveil Al$_{2}$O$_{3}$–Nb composite to form NbO, whereas for Al$_{2}$O$_{3}$–Ta the ternary compound aluminum tantalate (AlTaO$_{4}$) is found. Thermodynamic calculations show that the changing oxygen solubility in Nb accounts for the formation of NbO, and explain the absence of a corresponding niobate (AlNbO4) phase. AlTaO$_{4}$ is identified as the disordered tetragonal high-temperature modification

Structure of hydrated calcium carbonates: A first-principles study

The structures of both ikaite (CaCO3·6H2O) and monohydrocalcite (CaCO3·H2O) were computed at the PBE0 level of theory, using all electron Gaussian type basis sets. Correction for the long-range dispersion contribution was included for the oxygen–oxygen interactions by using an additive pairwise term with the atomic coefficients fitted against the calcite vs aragonite enthalpy difference. The potential chirality of monohydrocalcite is discussed, as well as the helical motifs created by the three-fold rototranslational axes parallel to the [001] direction. These elements represent a significant link between monohydrocalcite and vaterite, both appearing as intermediate species during CaCO3 crystallization from amorphous calcium carbonate. The hydrogen bond pattern, never fully discussed for monohydrocalcite, is here described and compared to the available experimental data. Both phases are characterized by the presence of hydrogen bonds of moderate to high strength. Water molecules in monohydrocalcite interact quite strongly with 2 View the MathML source units through such hydrogen bonds, whereas their interaction with each other is minor. On the contrary, water molecules in ikaite create a complex network of hydrogen bonds, where each water molecule is strongly hydrogen bonded to one View the MathML source anion and to one or two other water molecules